In an AC rotary machine used in an electric power steering device or the like, it is necessary to detect an angular position of a rotor of a motor with a high degree of precision in order to reduce a torque ripple in the motor. However, the detection precision of a magnetic sensor that detects the angular position of the rotor decreases due to the effect of a magnetic field generated by the motor itself.
In a conventional AC rotary machine for solving this problem, an improvement is achieved in the precision with which the angular position is detected by disposing a lid unit between an armature of the motor and the magnetic sensor so that the sensor is not affected by a magnetic field generated by the armature (see PTL 1, for example).
In another AC rotary machine, the magnetic sensor is configured to be capable of detecting a magnetic field generated by a sensor magnet with a high degree of precision by providing a magnetic induction unit in contact with a holder that holds the sensor magnet (see PTL 2, for example).
Furthermore, a conventional device serving as a resolver device achieves an improvement in the precision with which an angular position is detected by implementing frequency analysis on a speed signal while referring to an angle signal detected by a resolver in order to calculate a detection error for each frequency component, and correcting the angle signal using an estimated angle error signal obtained by synthesizing the detection errors (see PTL 3, for example).